I. Field of the Invention
The present invention relates to a solid-electrolyte cell and, more particularly, to a solid-electrolyte cell which uses a light metal as an anodic active material and a charge-transfer complex as a cathodic active material.
II. Description of the Prior Art
Solid-electrolyte cells both prevent electrolyte leakage and allow easy packaging into small units, since they use solid electrolytes. For these reasons, solid-electrolyte cells are increasingly used in compact electronic equipment. A conventional cathodic active material for such a solid-electrolyte cell is a material which is a mixture of a metal with an inorganic iodide such as lead iodide or bismuth iodide. However, in the cell which uses such an inorganic iodide-based material as a cathodic active material, the electromotive force significantly changes with changes in temperature. Thus, the cell of this type cannot provide stable characteristics.
Another type of solid-electrolyte cell has been recently proposed which uses a charge-transfer complex containing iodine as an electron acceptor in place of the inorganic material as described above. In a cell of this type, a light metal as an anodic active material is in contact with the charge-transfer complex as the cathodic active material. The solid electrolyte is, in this case, a light metal iodide which is formed in situ at the interface between the anodic and cathodic active materials by the reaction between the light metal and the electron acceptor (i.e., iodine) of the charge-transfer complex. Since iodine is an electron acceptor, the voltage of the anodic active material is as high as about 2.8 V. Since the cathodic active material is itself a charge-transfer complex, it has electron conductivity. Furthermore, since iodine is taken in within the structure of the charge-transfer complex, the iodine vapor pressure is reduced and corrosion of the cell materials is reduced to the minimum. For these reasons, a charge-transfer complex containing iodine as an electron acceptor is expected to be a promising cathodic active material.
Known examples of an electron donor which, together with iodine, constitutes the charge-transfer complex include nitrogen-containing compounds such as phenothiazine, poly(2-vinylpyridine), 1-ethylpyridine, or tetramethylammonium; and polycyclic compounds such as pyrene or perylene. However, a charge-transfer complex containing one of these compounds as an electron donor and iodine as an electron acceptor does not provide satisfactory iodine vapor pressure and electron conductivity. Thus, such as charge-transfer complex will not in practice provide satisfactory characteristics (discharge properties and long service life of a cell) when used as a cathodic active material of a solid-electrolyte cell. Furthermore, most of these charge-transfer complexes have poor film formability and flexibility; films of these complexes easily crack during manufacture of cells, providing only a low manufacturing yield.